Magnetic Random Access Memory (xe2x80x9cMRAMxe2x80x9d) is a non-volatile memory that is being considered for short-term and long-term data storage. MRAM has lower power consumption than short-term memory such as DRAM, SRAM and Flash memory. MRAM can perform read and write operations much faster (by orders of magnitude) than conventional long-term storage devices such as hard drives. In addition, MRAM is more compact and consumes less power than typical hard drives.
An MRAM device may include an array of memory cells, in which each memory cell includes a magnetic tunnel junction. A first logic value maybe written to a selected memory cell by setting its magnetic tunnel junction to a parallel magnetization orientation, or a second logic value may be written to the selected memory cell by setting its magnetic tunnel junction to an anti-parallel magnetization orientation.
The magnetization orientation affects the resistance of the magnetic tunnel junction. Generally, a magnetic tunnel junction has a nominal resistance (RN) when its magnetization orientation is parallel, and a higher resistance (RN+xcex94RN) when its magnetization orientation is anti-parallel. The ratio xcex94RN/RN is referred to as the tunneling magnetoresistance ratio (TMR) of the magnetic tunnel junction.
The logic value stored in a memory cell may be read by sensing the resistance state of the magnetic tunnel junction. However, the TMR of a typical magnetic tunnel junction tends to be relatively low. The low TMR can make it difficult to distinguish between the two resistances. Thus the low TMR reduces the reliability of reading the stored logic value.
It would be desirable to increase the reliability of reading memory cells based on magnetic tunnel junctions.
According to one aspect of the present invention, a magnetic memory device includes a first magnetic tunnel junction including a first reference ferromagnetic layer; a second magnetic tunnel junction including a second reference ferromagnetic layer; and an electrically conductive spacer layer between the first and second reference layers. The first and second reference layers are antiferromagnetically coupled. Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention.